Of course, you can enter in "Secret Base" from a hatch..., but...You can move into "Secret Base" with "Secret Base Teleporter" from anywhere momentarily, and can return to the previous place again.

1. When FONV starts, "Secret Base Teleporter" is added into your inventory at armor section automatically. 2. When you equip "Secret Base Teleporter", You move into "Secret Base" immediately. 3. When you unequip "Secret Base Teleporter", You return to the previous place immediately.